From 0f56e66e2f53df9e66c87c4c703a093c7926dc1c Mon Sep 17 00:00:00 2001 From: phk Date: Wed, 10 Mar 2004 20:41:09 +0000 Subject: Fix a long-standing deadlock issue with vnode backed md(4) devices: On vnode backed md(4) devices over a certain, currently undetermined size relative to the buffer cache our "lemming-syncer" can provoke a buffer starvation which puts the md thread to sleep on wdrain. This generally tends to grind the entire system to a stop because the event that is supposed to wake up the thread will not happen until a fair bit of the piled up I/O requests in the system finish, and since a lot of those are on a md(4) vnode backed device which is currently waiting on wdrain until a fair amount of the piled up ... you get the picture. The cure is to issue all VOP_WRITES on the vnode backing the device with IO_SYNC. In addition to more closely emulating a real disk device with a non-lying write-cache, this makes the writes exempt from rate-limited (there to avoid starving the buffer cache) and consequently prevents the deadlock. Unfortunately performance takes a hit. Add "async" option to give people who know what they are doing the old behaviour. --- sbin/mdconfig/mdconfig.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'sbin/mdconfig/mdconfig.c') diff --git a/sbin/mdconfig/mdconfig.c b/sbin/mdconfig/mdconfig.c index 6296da7..b23e903 100644 --- a/sbin/mdconfig/mdconfig.c +++ b/sbin/mdconfig/mdconfig.c @@ -117,7 +117,11 @@ main(int argc, char **argv) case 'o': if (cmdline != 2) usage(); - if (!strcmp(optarg, "cluster")) + if (!strcmp(optarg, "async")) + mdio.md_options |= MD_ASYNC; + else if (!strcmp(optarg, "noasync")) + mdio.md_options &= ~MD_ASYNC; + else if (!strcmp(optarg, "cluster")) mdio.md_options |= MD_CLUSTER; else if (!strcmp(optarg, "nocluster")) mdio.md_options &= ~MD_CLUSTER; -- cgit v1.1